Entrainment of a gas in a liquid is required in numerous industrial processes, typically for the purposes of reacting the gas with such liquid or materials in such liquid, such as dissolved ions or finely dispersed solids, to cause reaction of such gas with materials therein to cause same to be neutralized by, react with, or precipitate or be filtered out of such liquid.
For example, it is known to bubble ozone through water, to allow the ozone to react and combine with dissolved minerals and/or finely dispersed solids within the water, so as to form solid products which may either precipitate out of the liquid or be filtered from the water, so as to thereby purify the water. The ozone may further react with harmful bacteria or the like in the water so as to render them harmless or odourless.
Where a gas is desired to react with a liquid or finely dispersed solids in such liquids, it is widely known that small bubbles of gas immersed in such liquid will have, for the same volume of gas, a greater surface area and thus a greater liquid/gas interface, than the same volume of gas when such gas exists in larger bubbles.
A large gas/liquid interface is a desirable characteristic in instances where the gas is introduced into a liquid for the purposes of reacting the gas with the liquid or dispersed solids in such liquid, since greater surface area of the gas exposed to such liquid and/or finely dispersed solids in such liquid decreases the time it takes for the gas to react with the liquid or finely dispersed solids within such liquids, thus allowing quicker processing. As well, a lesser amount of gas, and smaller containment vessels, can thus be used, resulting in cost savings.
The benefits, therefore, of introducing or entraining very small bubbles of gas, typically in the range of 50 to 100 microns in diameter, into a liquid for the purposes of increasing the surface area of the gas relative to the liquid (and/or finely dispersed solids in such liquid) are known. Small bubbles of this size are generally referred to in the art as microbubbles. For the purposes hereinafter of this disclosure, microbubbles will be referred to and will be understood as meaning gas bubbles of a diameter in the range of 50 to 100 microns, and preferably 5 to 50 microns.
A number of devices and methods for aerating liquids, typically water, with gas bubbles, are known.
For example, U.S. Pat. No. 2,890,838 teaches a device for filter-separating iron from water. Water is delivered via a pipe 13 to an air aspirator 14, and thereafter such water having air entrained therein is delivered via pipe 16 to the upper portion of a tank 10, where it passes vertically downwardly in the tank 10 to a spray valve 19. At the spray valve 19 the water-air mixture flows outwardly through openings 21 into chamber 22 formed in a cylindrical hollow body 23 mounted on valve 19. The upper end of the body 23 is cone shaped, and contacts the mating lower cone-shaped end 25 of valve body 26. The water-air mixture flows upwardly and outwardly through the cone-shaped opening formed between cone-shaped surfaces 24, 25 in the form of a vaporized spray S, as shown in FIGS. 2 & 4 thereof, and mixes with the air in the tank 10 as it strikes the underside 27 of the top 28 of the tank 10, thereby introducing air into the liquid which in turn oxidizes metabolic iron present in the water. Iron precipitates then settles out of solution and down through the water contained in tank 10.
U.S. Pat. No. 5,601,724 and U.S. Pat. No. 5,460,731 teach an apparatus and method, respectively of aerating liquids. FIGS. 1 & 2 of each of '724 and '731 show a venturi air injector 10 used to inject air into water in a conduit 12. Such air-water mixture enters the bottom portion of a tower-like pressure vessel 14, where it is directed upwardly via conduit 30, where it is directed through a cylindrical restriction gap 19 formed between the second end 34 of conduit 30 and the top 18 of vessel 14. The gas, being of lesser density, passes more quickly through the restriction, thereby accelerating the liquid. As the liquid exits the restriction gap 19 it pneumatically hammers against the top 18 of pressure vessel 14. Thereafter the liquid stream, by force of gravity, cascades through the gas in pressure vessel 14 downwardly to further impact plate 35. Thereafter the liquid stream then passes through openings 37 in plate 35 and by force of gravity cascades through the gas in pressure vessel 14 to further impact on liquid at the bottom of the vessel. Thereafter such liquid, having small bubbles of air entrained therein, is removed via a conduit from the bottom of vessel 14.
U.S. Pat. No. 5,096,596 to a “Process and Apparatus for Removal of Mineral Contaminants from Water” teaches a pressurized aeration tank 24 having a tube 26 located within said tank 24 which supplies the tank 24 with raw water, which is introduced to the tank 24 via the tube 26 via a plurality of holes 28 in the tube (ref col. 2, lines 49-54 and FIGS. 1-7). The tube 24 only supplies “raw water” and not water having air bubbles entrained therein, and is not for the purpose of providing gas microbubbles of a range of 5-50 microns. Most importantly, no relationship regarding the size of the holes 28 in the tube 24 is specified to attempt to attain microbubbles, even if the patent further provided for the raw water to first have bubbles introduced therein.
U.S. Pat. No. 4,556,523 teaches a microbubble injector usable to separate material of different density by flotation, wherein microbubbles of gas are introduced into a chamber 14 containing a liquid mass 16. As may be seen from FIG. 1 of US '523, a gas admixture device 4 receives air through an inlet 6 and ordinary water through an inlet 8. The resulting air-water mixture is supplied by a conduit to the bottom of chamber 14, where it passes through an injector wall 10 via an injector hole 12 to procure a high velocity jet of air water. A deflector wall 18 is disposed over such injector hole, so as to create a narrow gap around the injector hole, which the water/air mixture must pass through. The injector hole is preferably substantially circular, and the height of the passage between the injector and deflector wall at the edge of the injector hole is less than one quarter of the diameter of the injector hole in the injector wall.
Disadvantageously, none of the aforementioned patents teach or disclose any specific design interrelation between the dimensions of the injector holes/parts/or gaps and the conduit outer dimensions which will best produce microbubbles in the liquid
For example, US '838 simply provides a nut 23 on the end of the valve 24 to adjust the size of the aperture between cone surfaces 24,25 through which the water must pass. No gap dimension is ever specified which best provides bubbles of a desired small size.
Similarly, each of US '724 and '731 simply disclose that the size of the restriction gap 19 required is dependent upon the size of the bubbles that are produced, with no direction as to what gap size will produce microbubbles in the range of less than 100 microns. These two patents each go on to note that (at col. 6, lines 44 to 47) that the greater the diameter of the cylindrical edge, the closer the end of conduit 30 had to be positioned to the top 18 of the pressure vessel 14 (i.e. the smaller the restriction gap had to be) in order to form bubbles of the desired size. No desired size of bubbles was ever identified, nor was there ever any relationship specified between the gap size and the diameter of the pipe, which would produce the smallest bubbles, namely microbubbles of diameter in the 5-100 micron range.
U.S. Pat. No. 4,556,523 perhaps comes closest to specifying an interrelation between the components in order to achieve desired small microbubble size in the range of 50 to 100 microns, specifying as noted above that the passage between the injector and deflector wall at the edge of the injector hole is less than one quarter of the diameter of the injector hole in the injector wall. No specific optimum size was specified Moreover, the particular manner by which the microbubbles are created, namely requiring an injector wall 10 and deflector wall 14, requires substantial quantity of material, and is thus a particularly material-intensive design and thus relatively costly.
Accordingly, a clear and real need exists for an aeration apparatus of simple and relatively inexpensive design having a configuration wherein the size of the flow aperture(s) through which a gas/liquid mixture flows can be accurately designed so as to give microbubbles of the desired small size.